Metering systems generally provide a controlled flow of fluid from a fluid reservoir. Various metering systems are known in the art for controlling and metering the flow of fluids, such as sealants, adhesives, epoxies, and the like. It is also known to combine two or more metering systems together to control the flow of two or more component fluids so that they are mixed together in a pre-determined ratio. These types of mixing systems are commonly used in various industries to mix and dispense two-component fluids, such as epoxies, which, for example, may comprise a catalyst fluid and a resin fluid that must be mixed in a pre-determined ratio.
FIG. 4 schematically illustrates a known mixing system, comprised of two metering systems 400 and 401, for mixing two component fluids in a pre-determined ratio and dispensing the mixed fluid. With respect to metering system 400, a first component fluid is stored in a first fluid reservoir or container 351. A pump 353 causes the fluid to flow through input conduit 303. Valves 301A and 301B control the flow of the first fluid into a metering cylinder 311. A piston 309 is slidably disposed in the cylinder 311. Input valves 301A and 301B are three-way valves that have three mutually-exclusive modes of functionality. For illustration purposes, these three modes are described in connection with valve 301A. First, the valve can be turned off, which prevents fluid from flowing through the valve in any direction. Second, valve 301A can permit fluid to flow from input conduit 303 through conduit 302A and into metering cylinder 311. Third, the valve 301A can permit fluid to flow from metering cylinder 311 into output conduit 304A. The valve mode is controlled by valve operator 310A. The functionality of valve 301B is identical to valve 301A. Generally, when valve 301A permits fluid to flow into metering cylinder 311, valve 301B allows fluid to flow from the metering cylinder 311 into the output conduit 304B. During this mode of valve operation, piston 309 is moving from left to right (in FIG. 3) to force fluid from the right side of the metering cylinder 311 into output conduit 304B and provide additional volume on the left side of cylinder 311 for the fluid coming in through valve 301A. When piston 309 reaches the right end of cylinder 311, piston 309 switches direction. Valve 301A changes mode to permit fluid to flow from the left side of cylinder 311 into output conduit 304A, and valve 301B changes mode to permit fluid to flow from input conduit 303 into the right side of cylinder 311.
Two of the described metering systems can be used together to mix two component fluids into a single mixed fluid, as shown in FIG. 3. Metering system 401 is identical in assembly and operation to metering system 400. The first component fluid flowing through output conduit 305 is mixed with the second component fluid flowing through conduit 306 in a mixer device (not shown), and the mixed fluid is dispensed therefrom. The output fluid can be applied to a variety of work pieces, such as automobiles and automobile components for example. By varying the relative sizes of the metering cylinders 311 and 312, the two component fluids can be mixed in a pre-defined ratio. Similarly, multiple metering systems can be used together, as described above, to meter and mix three, four, or five part fluids into a single mixed fluid.
The inventor hereof has recognized that the above-described metering and mixing system lacks operational flexibility. Specifically, the use of three-way valves 301A and 301B do not allow the system to control the flow of fluid with utmost flexibility and robustness. Further, the inventor has recognized that the use of three-way valves in metering systems is not optimal for some applications, such as for metering fluids having abrasive particles, particularly at high pressures, because they do not wear as well as two-way valves. Further, the inventor has recognized that the use of three-way valves in metering systems that dispense fluids at high pressures is not optimal because the high fluid pressure tends to force the plastic casing of the valves away from the valve ball, thereby allowing fluid to pass through the valve even when the valve is in its “off” position. Accordingly, the inventor has developed a new metering and mixing system that provides more operational flexibility, as well as more resistance to wear, than known metering and mixing systems.